logging: log to file

New env var CTOP_DEBUG_FILE to specify a path to log file

.gitignore

@@ -1,3 +1,4 @@
 ctop
 .idea
-/vendor/
+/vendor/
+*.log

_docs/debug.md

@@ -54,3 +54,18 @@ CTOP_DEBUG=1 CTOP_DEBUG_TCP=1 ./ctop
 ```
 
 A TCP listener for streaming log messages will be started on the default listen address(`0.0.0.0:9000`)
+
+## Log to file
+
+You can also log to a file by specifying `CTOP_DEBUG_FILE=/path/to/ctop.log` environment variable:
+```sh
+CTOP_DEBUG=1 CTOP_DEBUG_FILE=ctop.log ./ctop
+```
+
+This is useful for GoLand to see logs right in debug panel: 
+* Edit Run configuration 
+* Go to Logs tab
+* Specify this log file in "Log file to be shown in console".
+Then during debugging you'll see the log tab in debug panel:
+
+![Debug in GoLand](img/goland_debug.png)

logging/main.go

@@ -29,6 +29,7 @@ type statusMsg struct {
 type CTopLogger struct {
 	*logging.Logger
 	backend *logging.MemoryBackend
+	logFile *os.File
 	sLog    []statusMsg
 }
 
@@ -58,6 +59,7 @@ func Init() *CTopLogger {
 		Log = &CTopLogger{
 			logging.MustGetLogger("ctop"),
 			logging.NewMemoryBackend(size),
+			nil,
 			[]statusMsg{},
 		}
 
@@ -68,7 +70,22 @@ func Init() *CTopLogger {
 		backendLvl := logging.AddModuleLevel(Log.backend)
 		backendLvl.SetLevel(level, "")
 
-		logging.SetBackend(backendLvl)
+		logFilePath := debugModeFile()
+		if logFilePath == "" {
+			logging.SetBackend(backendLvl)
+		} else {
+			logFile, err := os.OpenFile(logFilePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0666)
+			if err != nil {
+				logging.SetBackend(backendLvl)
+				Log.Error("Unable to create log file: %s", err.Error())
+			} else {
+				backendFile := logging.NewLogBackend(logFile, "", 0)
+				backendFileLvl := logging.AddModuleLevel(backendFile)
+				backendFileLvl.SetLevel(level, "")
+				logging.SetBackend(backendLvl, backendFileLvl)
+				Log.logFile = logFile
+			}
+		}
 
 		if debugMode {
 			StartServer()
@@ -105,8 +122,12 @@ func (log *CTopLogger) tail() chan string {
 
 func (log *CTopLogger) Exit() {
 	exited = true
+	if log.logFile != nil {
+		_ = log.logFile.Close()
+	}
 	StopServer()
 }
 
-func debugMode() bool    { return os.Getenv("CTOP_DEBUG") == "1" }
-func debugModeTCP() bool { return os.Getenv("CTOP_DEBUG_TCP") == "1" }
+func debugMode() bool       { return os.Getenv("CTOP_DEBUG") == "1" }
+func debugModeTCP() bool    { return os.Getenv("CTOP_DEBUG_TCP") == "1" }
+func debugModeFile() string { return os.Getenv("CTOP_DEBUG_FILE") }